PROJECT SUMMARY/ABSTRACT In this project we propose to complete development and performance evaluation of a smartphone-based mobile medical application (EyeTurn) for use by eye-care professionals and lay people to screen for strabismus (eye misalignment). Strabismus develops in an estimated 3-8% of the U.S. population and is a leading risk factor for amblyopia in young children. Early detection and treatment are critical to prevention of permanent vision losses, yet only 40% of U.S. children under age 6 reportedly receive vision screening. In the elderly and in head trauma populations where the prevalence is highest, untreated strabismus can result in postural instability, leading to a significantly greater risk of devastating falls. However, significant barriers of cost and availability of trained examiners limit access to strabismus screening for at-risk populations, especially in under-served rural and low-income areas and elder care facilities. The novel EyeTurn app provides the first image-based tool for eye alignment testing by lay persons without reliance on a costly device. We propose to further develop the EyeTurn app to improve reliability of automatic eye detection and vertical strabismus measurement, add HIPAA-compliant patient data management, improve the operator interface for cover- uncover testing and for screening/home use, and incorporate modules for user training, patient education, and doctor finding. We will evaluate EyeTurn performance relative to standard test methodology in targeted populations likely to contain subjects who are difficult to accurately measure, including both young children and head trauma or low vision patients. We will also report initial estimates of EyeTurn sensitivity and specificity in a pilot-scale application to pediatric screening. At the conclusion of the Phase II project, we will have demonstrated accuracy, reliability and effective range comparable to or exceeding costly tests now employed in strabismus screening. Bringing this low cost product to wide commercial availability, we could make possible a paradigm shift in cost-benefit calculations for strabismus screening and measurement globally, resulting in greater access to treatment for strabismus-affected individuals. A demonstrated effectiveness for use by vision care professionals will position EyeTurn to apply for FDA pre-market approval and perform clinical trials in support of use by lay people for strabismus screening.